1. Field
The following description relates to a transparent electrode including graphene oxide and carbon nanotube, a conductive thin film including a transparent electrode, and a method of preparing such a transparent electrode or such a conductive thin film. The description also relates to, for example, a method of preparing a conductive thin film made of a reduced graphene oxide and a carbon nanotube, and a transparent electrode including a conductive thin film prepared by the same method. The following description further relates to a method of preparing a conductive thin film made of a reduced graphene oxide and a carbon nanotube, which enables the use of a low temperature process and mass production and can improve both electrical conductivity and transparency, and a transparent electrode including the conductive thin film prepared by the same method.
2. Description of Related Art
A transparent electrode is being widely used in various electronic devices, which require both a light transmission characteristic and electrical conductivity. Examples of such electronic devices include image sensors, solar cells, liquid crystal display devices, organic EL displays and touch screen panels. The transparent electrode consists of a transparent substrate and a conductive film formed on the transparent substrate. For the conductive film, an indium thin oxide (ITO), which facilitates formation of a thin film and has an excellent light transmission characteristic and electrical conductivity, has been mostly used. However, using ITO is undesirable in certain cases because ITO requires high preparation costs, and because ITO exhibits low flexibility which may increase surface resistance and deteriorate the durability of the finished product, for example, as when ITO is used in a flexible display.
Accordingly, attempts to apply low dimensional materials, which have high electrical conductivity while being flexible, such as a carbon nanotube and graphene, to the transparent electrode have recently increased. However, if a conductive thin film made of only the carbon nanotube is used for a transparent electrode under the same conditions, the electrical conductivity is low, compared to the excellent transparency, due to impurities caused from the preparation process or the raw material itself. If a conductive thin film made of only graphene is used for a transparent electrode, the electrical conductivity is relatively fine, compared to the carbon nanotube, but the transmittance is low. In order to resolve the problems, there has been an attempt to improve the electrical conductivity by using a combined material of carbon nanotubes and graphenes to effectively connect empty spaces between the carbon nanotubes and the graphenes through a line contact between the carbon nanotubes and a surface contact between the graphenes. However, in the technology for bulk synthesis of graphenes that has been known to the present, the mass production has been difficult due to restriction to use of a reducing agent, low efficiency, impurities included, and other causes. Especially, in case of reducing a graphene oxide by using known reducing agents such as hydrazine hydrate, sodium borohydrate (NaBH4) and sulfuric acid (H2SO4), a reaction at a high temperature is required. Thus, there has been the problem that the conductive film cannot be applied to a flexible substrate.